1. Field of Invention
The present invention relates to an inverter-type power supply for the magnetron in a microwave oven.
2. Prior Art
A magnetron has a thermionic cathode that must be brought to incandescence before the magnetron is properly operable to receive its main operating power.
When, as frequently is desirable to do, a magnetron is powered by way of being effectively parallel-connected with the tank capacitor of a high-Q resonant circuit that is series-excited by the voltage output of an inverter power supply, a problem arises: before the magnetron's cathode has reached incandescence, the magnetron is not properly operative to absorb power; which means that the high-Q resonant circuit is effectively unloaded and therefore represents an effective short circuit across the inverter's voltage output. This not only causes an excessively large power drain from the inverter, but also causes excessively large-magnitude voltages to develop across the circuit elements of the resonant circuit.
One way of circumventing this problem is that of providing the requisite cathode heating power from a separate source of power, and to delay the turning-on of the inverter power supply until after the magnetron's cathode have reached incandescence. However, this approach requires the use of an extra power supply, and is therefore not as cost-effective as might be desired.